A show about a man plucked from obscurity who has to adjust quickly when thrust amongst the nobility was saved last night by an understudy, Ryan Pidgen, who with very little notice, was similarly thrust center stage after leading man Matt Lucas (of Little Britain fame) had to withdraw, very unusually, from the opening (and press) night because of throat problems.

Despite, one presumes, very little rehearsal, Pidgen commanded the stage with a great physical ease, a warm voice and natural comic gifts, an astonishing rescue job with no signs of any slip ups. Although an experienced performer this deserves to propel him to the front rank.

This is Daniel Evan's revival of Noel Gay's creaky 1937 hit which was last in the West End in the '80s when Stephen Fry did some lucrative surgery on the book, and Robert Lindsay and Emma Thompson, no less, stole the show as the Cockney leads. It ran for 8 years in London and when it transferred to Broadway Lindsay took the Tony.

It is great to see it back and Evans imbues it with pluck and energy and the lightness of touch it needs. Alistair David's choreography too is witty, nuanced and crowd pleasing all at the same time. It's essentially a 1930s Hollywood musical, albeit one whose influences are totally in English Music Hall, whose main purpose is to cheer us all up and make sure we skip out humming the great earworm melodies ('Lambeth Walk', 'The Sun Has Got His Hat On', 'Leaning on a Lamppost' all feature).

The quickfire Cockney gags are a delight too, such as when butler proffers a tray of drinks to Bill asking "Aperitif, M'Lud?" to which he responds "No fanks, I've got me own" pointing to his teeth.

The plot, oddly, has an underdeveloped beginning (not clear why these warring hangers-on had to make him the offer) and a rushed ending, where the piece drastically changes gear from frivolous fun to romantic dirge. There are too many longueurs but Evans, quite rightly, throws the spotlight on the production numbers.

Chirpy Cockney costermonger Bill Snibson (Pidgen) is proclaimed the long-lost heir to the Earl of Hareford but he's not posh enough to gain the approval of the executor of the will - the daunting Duchess of Dene (Caroline Quentin). He ends up trapped between two worlds, increasingly isolated by both and forced to choose between his Lambeth sweetheart Sally (Alex Young) and his new life of luxury. It's another Pygmalion story as he too must learn lose his cockney vowels and play the part of the aristocrat.

Along the way there's a tap dancing family solicitor Parchester (Jenny Dale) who is also a soprano and serves as a running gag and Clive Rowe who weaves his usual musical theatre gold in a supporting role as a friend of the family who has long held a candle for the Duchess. From her many TV hits we knew Quentin has comic finesse but here she also reveals an attractive singing voice. Alex Young is rather underpowered as Sally but Siubhan Harrison has more fun as the gold digging aristo Lady Jacqueline.

The other star of the evening is Gareth Valentine's work on the score and as MD. He gives it all a lick of paint and his orchestrations enhance Gay's simple tunes with lush elements of swing music and Latin, and witty sidelines into everything from Handel to Gershwin. It's a stunning adornment to a piece which needs it.